Canvas, Wools, Shade Cards, Needles etc:   Appleton Wools (as used by William Morris) plus everything else, including helpful advice.
Lenham Needlecraft:

Chip Foam:   Reconstituted chip foam can often be supplied by a local upholsterer but emphasise the need for it to be 10lb quality.  This should last for 40-50 years.  Some suppliers try to tell you that 6lb chip foam is suitable.  It is not.  It will collapse in less than 20 years and most people find it too squashy.
Pentonville Rubber Company

Sundries:   You can almost certainly find local suppliers for hard-wearing cloth for the base of your kneelers, strong thread for making them up and nylon tape for hanging them, but if in difficulty try the following:
Heavy calico or similar from The Cloth Shop:
Tape and strong thread from Macculloch and Wallis:
D rings from your local hardware shop or Amazon.
Curtain rings from your local haberdasher or Amazon.

Software:   Software can be useful for copying photographs and for giving stitchers a coloured design to work from.  PCStitch has been used successfully by some congregations recorded on this website.  Let us know of other useful software suppliers.
PC Stitch